1. Field of the Invention
The present invention relates generally to optical fiber Bragg grating (FBG) sensors, specifically to incorporating particles into FBG sensors for magnetic field sensing, and most specifically to incorporating particles into the core and cladding of FBG sensors so that magnetic fields directly shift the reflected wavelength of light associated with an FBG sensor system.
2. Description of the Related Art
FBG sensors are made by “inscribing” or “writing” the periodic variation of refractive index into the core of a special type of optical fiber using an intense ultraviolet (UV) source such as a UV laser. This creates a grating that reflects a particular wavelength of light while transmitting others.
Over the past decade, optical FBG sensors have been used to measure a variety of physical characteristics such as temperature, strain, and pressure. Several inventions have been developed that attach magnetic materials directly or indirectly to an optical fiber containing Bragg gratings so that when such a fiber is subjected to a magnetic field, the magnetic materials subject the fiber to a physical deformation, which, in turn, can be measured by monitoring the strain-induced shift in reflected wavelength.
For example, see the following: U.S. Pat. No. 7,195,033 which discloses a fiber optic sensor scheme including magnetic sleeve that deforms the fiber in order to determine the position of the sleeve; U.S. patent application 2010/0316328 which discloses a fiber optic position transducer attached to a magnetic element to control a flow valve via a magnetic field; and, a paper presented at the 1st International Conference on Sensing Technology, 2005, Palmerston, North New Zealand titled “Novel Magnetic Sensor Based on Fiber Bragg Grating and Magnetic Shape Memory Alloys” discloses bonding a FBG optical sensor system to a piece of shape memory alloy in order to deform the optical fiber via a magnetic field.
It has also been shown that a magnetostatic wave can have an effect on optical wavelength in an optical system. For example, see U.S. Pat. No. 4,575,179 that discloses an optical signal processor device that employs a magnetorestrictive thin film, biased by a magnetic film that is placed within the path of an optical beam in order to diffract the beam.
However, a magnetic material has not been incorporated within an optical fiber itself in order to modify the optical wavelength of a fiber optic FBG system using a magnetic field.
Therefore, it is desired to provide an optical fiber with FBGs having a magnetic material incorporated directly within the fiber in order to modify the optical wavelength of the system through a magnetic field.